The present invention relates to a method and apparatus for the production of composite filter plugs which can be used in the manufacture of filter cigarettes, cigars or cigarillos. The invention also relates to a method and means for controlling the production of composite filter plugs of the type wherein a tubular wrapper consisting of cigarette paper, imitation cork or other suitable flexible wrapping material surrounds two or more different filter rod sections.
Composite filter plugs are produced in apparatus wherein an assembling unit forms a continuous rod-like filler consisting of alternating filter rod sections of two or more different types. The filler is moved lengthwise and is wrapped into a web of cigarette paper or the like to form with the web a continuous filter rod which is severed by a cutoff to yield a file of discrete composite filter plugs each of which contains at least a portion of one or more filter rod sections of each type. For example, a composite filter plug may contain a centrally located first filter rod section of double unit length which consists of acetate fibers and two second filter rod sections of unit length which flank the centrally located first section and consist of acetate fibers interspersed with charcoal, crepe paper or other suitable filter material. Such filter plugs are thereupon assembled with pairs of plain cigarettes of unit length to form therewith filter cigarettes of double unit length wherein the filter plug is located midway between two plain cigarettes of unit length. Each filter cigarette of double unit length is thereupon severed midway across its filter plug to yield two filter cigarettes of unit length each of which includes a plain cigarette of unit length and a relatively short filter plug containing one-half of the respective first filter rod section and one of the respective second filter rod sections.
A drawback of presently known apparatus for the production of composite filter plugs is that the cutoff does not and cannot invariably sever the filter rod in such a way that the composition of each and every filter plug is the same. Thus, it can happen that the first filter rod section is not located exactly midway between the two second filter rod sections, i.e., that the length of one second filter rod section exceeds the length of the other second filter rod section and the filter plug further contains a portion of an additional first filter rod section. Such filter plugs are considered defective and, if detected, must be segregated from satisfactory filter plugs prior to introduction into a machine for the manufacture of filter cigarettes.
Similar but less serious problems arise in machines for the production of plain cigarettes wherein certain portions of the rod-like tobacco filler contain more tobacco than the others, e.g., wherein the ends of the filler contain more tobacco (and are denser) than the median portion of the filler. The cutoff must sever the cigarette rod midway across each densified filler portion to thereby insure that both ends of the filler in each and every cigarette will contain more tabacco than the central portion of the filler. As a rule, the means for monitoring successive densified portions of the filler comprises a detector including a source of corpuscular radiation, e.g., a beta ray detector. Reference may be had to U.S. Pat. No. 3,604,430 which further mentions the possibility of resorting to a capacitive detector. The proposal to use capacitive detectors in connection with cigarette rods wherein filler portions of greater density alternate with much longer filler portions of lesser density is considered to be promising because the detector must monitor a single type of material (tobacco) and also because the length of filler portions of lesser density normally greatly exceeds the length of filler portions of greater density. The length of the last mentioned filler portions is normally in the range of 10-12 millimeters. Moreover, the measurements need not be overly accurate because it is of no consequence whether or not the cutoff severs the filler exactly midway across successive portions of greater density. In fact, deviations amounting to 1-2 millimeters are quite acceptable in the manufacture of so-called dense end cigarettes. All the counts is to insure that the cutoff will sever the filler somewhere across the portions of greater density. The beta ray detector can be connected with a threshold circuit which transmits signals for effecting a change of the locus where the filler is severed when the intensity of signals received from the output of the detector exceeds a predetermined value. Such circuitry is incapable of insuring that the filler will be severed exactly midway across the portions of greater density; however, and as mentioned above, the accuracy is sufficient for the production of satisfactory or acceptable dense end cigarettes.
The situation is quite different in the production of composite filter plugs. First of all, various filter rod sections of the filler in a filter rod which is to be subdivided into composite filter plugs exhibit different dielectric constants. Secondly, the filter rod sections of the composite filler are very short so that a capacitive detector of finite length is not expected to furnish signals with a degree of reliability which is necessary to insure that each and every filter plug of a series of composite filter plugs will be identical with all other filter plugs. Otherwise stated, the aforementioned proposal in U.S. Pat. No. 3,604,430 (to use a capacitive detector as a substitute for a beta ray detector) does not allow for accurate determination of loci where a filter rod containing a composite rod-like filler should be severed by a cutoff in order to yield a succession of identical composite filter plugs. This is due to the fact that a capacitive detector is incapable of detecting the exact center of successive filter rod sections in the filler and/or the exact location of that region where two neighboring filter rod sections which consist of different filter materials abut each other. It is further known that signals furnished by a capacitive detector which is connected to a high-frequency source exhibit a tendency to drift; this phenomenon is another reason why a capacitive detector was considered to be impractical for use as a means for monitoring the constituents of the filler in a filter rod which is to be subdivided into composite filter plugs. In accordance with heretofore known proposals, the filler of such filter rod is monitored by a photoelectric detector which, however, is only suitable for the monitoring of so-called recessed filter plugs because the light beam issuing from the light source of the detector can pass through the gap between two spaced-apart sections of the filter plug. Such proposals failed to gain acceptance in the industry because the intensity of the light beam decreases considerably during passage through the wrapper of the filter plug so that the detector must utilize an extremely sensitive photoelectric transducer which is prone to malfunction, e.g., because it reacts immediately to the presence of minute solid particles, such as tobacco dust. Furthermore, the just discussed recessed filter plugs are not overly popular, i.e., filter cigarettes using such plugs consitute but a small percentage of currently produced filter cigarettes.
Photoelectric detectors are not suited for monitoring of filter rods wherein two or more different types of filter rod sections are disposed end-to-end because the transmissivity of filter rods varies very little or not at all. Therefore, certain presently known apparatus for the production of composite filter plugs employ detectors including sources of corpuscular radiation. Such detectors are reliable; however, they can be dangerous to attendants, especially to unskilled persons. Therefore, their use invariably involves a host of complex and expensive precautionary measures and, consequently, such detectors are not acceptable to many manufacturers of smokers' products. It is still prevalent to remove samples of composite filter plugs at regular or irregular intervals, to break open and visually examine the samples, and to manually adjust the apparatus if the examination of samples reveals deviations from an optimum composition. Such procedure is costly, time consuming and cannot prevent the manufacture of large quantities of unacceptable composite filter plugs.